Up to now, as a technique that identifies individual by conducting face recognition with the use of a plurality of sequential facial images, there are techniques disclosed in, for example, Patent Documents 1 to 3. First, Patent Document 1 discloses the installation and image capture conditions of a camera that can stably capture an image of a facial surface of a pedestrian.
FIG. 25 is a diagram illustrating an installation example of a pedestrian observation device disclosed in Patent Document 1. FIG. 25 is a diagram looking down at an entrance of a building from above. A person moves toward the entrance (between both of right and left walls 4001) (in a direction indicated by an arrow 4002). An essential observation area 4004 having a width A and a height B is set at a position over a pass line 4003 of the entrance connecting both of the right and left walls 4001 to each other, and the pass line 4003 is also set in the center of the essential observation area 4004. A direction and a field angle θ of a camera 4005 are set in the direction of the arrow 4002, which is a moving direction of the person, with respect to the pass line 4003. Also, a focal length of the camera 4005 is set between f and f+D illustrated in the figure. The conditions of “the camera installation position”, “the direction and field angle of the camera”, and “the focal length of the camera” are set so that the camera 4005 allows the essential observation area 4004 to fall within an image capture range, and can capture an image having the focal length within the image capture range. This makes it possible to stably capture the image of the face of the person who passes through the essential observation area 4004. Patent Document 1 discloses that an identification precision of the individual is improved by facially recognizing a plurality of images different in face direction, which are taken for the same person by a plurality of cameras.
On the other hand, Patent Document 2 and Patent Document 3 disclose a method in which a front image of the person is synthesized from a plurality of images different in face direction, which are taken for the same person by a plurality of cameras, through affine transform or field morphing, and face recognition is conducted by the aid of the synthesis result to identify the individual.
FIG. 26 is a diagram illustrating facial feature synthesis disclosed in Patent Document 2. FIGS. 26(A) and 26(B) illustrate facial images each having a different face direction, which are obtained by capturing an image of the same person from different cameras. Feature points of the face indicated by X-marks in the figures are detected by facial feature point search for the images of FIGS. 26(A) and 26(B). A front image illustrated in FIG. 26(C) is synthesized by affine transform on the basis of the detected facial feature point positions, and the face recognition is conducted by the aid of the synthesized front image to identify the individual.
In Patent Document 3, the front image is synthesized by not the affine transform but the field morphing, and the face recognition is conducted by the aid of the synthesized front image to identify the individual.